Secure system for allowing the execution of authorized computer program code

ABSTRACT

Systems and methods for selective authorization of code modules are provided. According to one embodiment, file system or operating system activity relating to a code module is intercepted by a kernel mode driver of a computer system. The code module is selectively authorized by the kernel mode driver by authenticating a content authenticator of the code module with reference to a multi-level whitelist. The multi-level whitelist includes (i) a global whitelist database remote from the computer system that contains content authenticators of approved code modules that are known not to contain viruses or malicious code and (ii) a local whitelist database containing content authenticators of at least a subset of the approved code modules. The activity relating to the code module is allowed when the content authenticator matches one of the content authenticators of approved code modules within the multi-level whitelist.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/155,218, filed Jan. 14, 2014, now U.S. Pat. No. 8,850,193, which is acontinuation of U.S. patent application Ser. No. 14/083,087, filed Nov.18, 2013, now U.S. Pat. No. 8,813,230, which is a continuation of U.S.patent application Ser. No. 13/912,454, filed on Jun. 7, 2013, now U.S.Pat. No. 8,589,681, which is a continuation of U.S. patent applicationSer. No. 13/438,799, filed on Apr. 3, 2012, now U.S. Pat. No. 8,464,050,which is a continuation of U.S. patent application Ser. No. 13/045,781,filed on Mar. 11, 2011, now U.S. Pat. No. 8,151,109, which is acontinuation of U.S. patent application Ser. No. 12/905,193, filed onOct. 15, 2010, now U.S. Pat. No. 8,069,487, which is a continuation ofU.S. patent application Ser. No. 11/296,094, filed on Dec. 5, 2005, nowU.S. Pat. No. 7,698,744, which claims the benefit of U.S. ProvisionalApplication No. 60/633,272, filed on Dec. 3, 2004, all of which arehereby incorporated by reference in their entirety for all purposes.

COPYRIGHT NOTICE

Contained herein is material that is subject to copyright protection.The copyright owner has no objection to the facsimile reproduction ofthe patent disclosure by any person as it appears in the Patent andTrademark Office patent files or records, but otherwise reserves allrights to the copyright whatsoever. Copyright© 2004-2014, Fortinet, Inc.

BACKGROUND

1. Field

Various embodiments of the present invention generally relate to systemsand methods for protecting computer systems and networks fromunauthorized code execution. More specifically, embodiments of thepresent invention provide for systems and methods of securing computersystems of subscribers to a cloud-based whitelist of a trusted serviceprovider by allowing only the execution of authorized computer programcode.

2. Description of the Related Art

The execution of unauthorized software has had a serious impact oncomputer users. The impact of unauthorized software execution not onlyapplies to malicious software, or malware, but also the use ofunlicensed software and software which may distract employees fromworking, such as music players, games, and/or the like.

Current approaches to dealing with these issues have proven ineffective.One common method of virus or malware detection is through the use ofsystem scans either initiated by the user or automatically schedule on aperiodic basis. During the scanning, the malicious software detector maysearch for traces of a virus or other malware using a database of knowmalware signatures. However, such databases must be routinely updatedand have generally proven ineffective against the next variation of thevirus.

Another common approach to dealing with malicious software execution isreal-time background system monitoring. Typically, this approachcontinuously monitors all incoming and outgoing files from the computersystem in order to determine any association with known malicioussoftware. Again, many of these approaches use a signature-based approachwhich is ineffective against the next variation of the malicioussoftware.

SUMMARY

Systems and methods are described for selective authorization of codemodules. According to one embodiment, file system or operating systemactivity relating to a code module is intercepted by a kernel modedriver of a computer system. The code module is selectively authorizedby the kernel mode driver by authenticating a content authenticator ofthe code module with reference to a multi-level whitelist. Themulti-level whitelist includes (i) a global whitelist database remotefrom the computer system that contains content authenticators ofapproved code modules that are known not to contain viruses or maliciouscode and (ii) a local whitelist database containing contentauthenticators of at least a subset of the approved code modules. Theactivity relating to the code module is allowed when the contentauthenticator matches one of the content authenticators of approved codemodules within the multi-level whitelist.

Other features of embodiments of the present invention will be apparentfrom the accompanying drawings and from the detailed description thatfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures, similar components and/or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label with a second label thatdistinguishes among the similar components. If only the first referencelabel is used in the specification, the description is applicable to anyone of the similar components having the same first reference labelirrespective of the second reference label.

FIG. 1 is a high level architectural diagram of a multi-level whitelistauthentication system for allowing the execution of authorized computercode in accordance with one embodiment of the present invention.

FIG. 2 illustrates an example of a computer system with whichembodiments of the present invention may be utilized.

FIG. 3 is a flow diagram illustrating an exemplary method for newprocess creation authorization processing in accordance with oneembodiment of the present invention.

FIG. 4 is an exemplary flow diagram illustrating a method forauthorization of loading of code modules by running processes inaccordance with one embodiment of the present invention.

FIG. 5 conceptually illustrates an exemplary multi-level whitelistdatabase system in accordance with one embodiment of the presentinvention.

FIG. 6 is a flow diagram illustrating a method of using a multi-levelwhitelist approach in accordance one embodiment of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention generally relate to systems andmethods for selective authorization of code modules. According to oneembodiment, a proactive whitelist approach is employed to secure acomputer system by allowing only the execution of authorized computerprogram code thereby protecting the computer system against theexecution of malicious code such as viruses, Trojan horses, spy-ware,and/or the like.

Various embodiments use a kernel-level driver, which intercepts or“hooks” certain system Application Programming Interface (API) calls inorder to monitor the creation of processes prior to code execution. Thekernel-level driver may also intercept and monitor the loading of codemodules by running processes, and the passing of non-executable codemodules, such as script files, to approved or running code modules viacommand line options, for example. The kernel-level driver makesdecisions regarding whether to allow code modules to be loaded (e.g.,mapped into memory) and/or executed based on whether the code modulesare “approved” as described in more detail below.

In one embodiment of the present invention, a kernel mode driverintercepts and monitors the loading of dependent code modules by runningprocesses. In some instances, the loading of a dependent code module bya running process represents an attempt by the running process to loadand execute the dependent code module within the address space of therunning process. In other instances, the loading of a dependent codemodule by a running process represents the passing of a non-executablecode module to the running module. Dependent code modules may includecode modules that can be loaded and executed from within an existingprocess (e.g., modules with a .dll extension) or non-executable codemodules (e.g., script files) that can be passed to a running process(e.g., a script interpreter). According to one embodiment, the kernelmode driver may take into consideration in connection with allowing ordenying the loading of the dependent code module, the identity or typeof the code module or running process that initiated the load request atissue. If the running process is a script interpreter, for example, thenthe dependent code module may be authenticated with reference to amultilevel whitelist architecture; however, if the running process is atext editor, then authentication of the dependent code module may bebypassed as there is no intent to run the script.

Various embodiments make use of a user-level service to augment theprocessing provided by the driver. Certain tasks, such as networkcommunication, are much more easily implemented in user-level code thanin a driver. While it is possible to implement all of the functionalityof this system in the driver, the preferred embodiment dividesprocessing between a user-level service process and the driver-levelgenerally along the lines of performing the most time sensitiveoperations directly in the driver and performing the more complexoperations at user-level.

Various features and/or advantages may be provided by one or moreembodiments of the present invention. These features and/or advantagesmay include the following: providing a secure system for limiting theexecution of computer program code to only that executable code whichcan be verified to be approved to run on that computer; and systems andmethods for protecting a computer system from attack by unauthorized ormalicious users or software attempting to modify the various whitelistdatabases or otherwise spoof the system such that unauthorized codewould be allowed to run.

According to one embodiment, a software package may be provided whichperforms one or more of the methods described herein. During theinstallation of the software on a computer system, the software modules(e.g., one or more of the kernel mode driver, OS file system activitymonitor, OS process creation activity monitor, OS module load activitymonitor, user mode service layer and user interface layer, etc.described below) are also installed. In some embodiments, a current copyof a global whitelist may be installed locally on the computer system.In addition, according to one embodiment, an inventory of the user'shard drive may be performed during which a content authenticator may becreated for each code module. For example, code modules may include, butneed not be limited to, files containing executable code, script files,batch files, dynamically-linked libraries (DLLs), executables, and/orthe like.

According to one embodiment, protection is not just limited totraditional executable modules but also extends to many kinds of‘script’ command/data files. The content authenticator may be comparedto those contained in one or more whitelists of varying scope. Forexample, some embodiments may use a multi-level whitelist architectureincluding one or more MRU caches, one or more global whitelists, and/orone or more local whitelists.

According to one embodiment, one or more whitelists may be protected bya digital signature of its own contents. The digital signature may bebased in part upon a hash value for the data in the whitelist. Thissignature may then be encrypted remotely by a Remote Signing Server(RSS) using public key cryptography. Then, each time one or more of thewhitelists are read into memory to look up a value during normaloperation, the hash value may be recalculated by the authenticationsystem software, and compared to the unencrypted stored value(unencrypted using the public key). If the two hash values compareequally, then it can be reasonably assured that the authenticatedwhitelist has not been modified maliciously.

In one embodiment, the RSS may be used to encrypt hash values of thewhitelists using Public Key Infrastructure (PKI) encryption, forexample. The RSS may host a secret (private) encryption key that it usesto encrypt values sent to it by client installations that are in need ofmodifying their database. Later a public key may be used to decrypt thevalue for comparison against calculated values allowing the code todetermine if any of the data has been modified.

Some embodiments additionally provide for a client verification scheme.According to one embodiment, the RSS verifies that a client making asignature request is indeed an actual approved instance of theauthentication system software, and not a hacker or someone attemptingto spoof the RSS. In order to do so, the system may make use a varietyof identifying information from the requestor to make thatdetermination. For example a machine ID, a password, and/or the like maybe used. A machine ID is a unique identifier (number) that is generatedat the time of authentication system software installation on an enduser computer or server. It may contain a globally unique identifier(GUID) in combination with some other values that uniquely identify thecomputer system that the client code was installed on (includingpossibly a CPU serial number, a network card unique media access control(MAC) address, and/or various other system information).

Various embodiments of the present invention may be used in either apersonal setting or within in a corporate network environment. The basictechnology for allowing/denying the execution of certain code modules isuseful for other purposes. In this manifestation, the user may not haveany control over approving or denying particular modules, but the ITmanager or department may. Instead of relying on a truly globalwhitelist, a custom whitelist database may be created and maintained bythe IT department. General operation of such an authentication system issimilar; however, less emphasis is given to an individual user's abilityto locally approve/reject modules.

In an enterprise setting, to better support centralized control overwhich modules are allowed to execute, it is anticipated that theauthentication system would include a ‘management console’ and that theauthentication system software is capable of beingcontrolled/configured/updated via remote control. Also, in thisenvironment it is desirable that the authentication system software beable to interface with other enterprise management tools. Therefore, inone embodiment, the authentication system software may be equipped witha remote control port to support such operations. Remote control of theauthentication system software may be subject tovalidation/authentication techniques to insure that only approvedmanagement consoles can control the authentication system software.

In addition to malware protection, other purposes and uses for acorporate version of the authentication system software may includeadditional features, such as one or more of: the ability to manuallylimit allowed applications on workstations within the network; theability to monitor and track software use activity; software licensemanagement; software use management, and/or the ability to aggregatedata from many computers on a network about how many copies of a certainsoftware application are being used at any one time.

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of embodiments of the present invention. It will beapparent, however, to one skilled in the art that embodiments of thepresent invention may be practiced without some of these specificdetails.

Embodiments of the present invention may be provided as a computerprogram product which may include a machine-readable medium havingstored thereon instructions which may be used to program a computer (orother electronic devices) to perform a process. The machine-readablemedium may include, but is not limited to, floppy diskettes, opticaldisks, compact disc read-only memories (CD-ROMs), and magneto-opticaldisks, ROMs, random access memories (RAMs), erasable programmableread-only memories (EPROMs), electrically erasable programmableread-only memories (EEPROMs), magnetic or optical cards, flash memory,or other type of media/machine-readable medium suitable for storingelectronic instructions. Moreover, embodiments of the present inventionmay also be downloaded as a computer program product, wherein theprogram may be transferred from a remote computer to a requestingcomputer by way of data signals embodied in a carrier wave or otherpropagation medium via a communication link (e.g., a modem or networkconnection).

While, for convenience, various embodiments of the present invention maybe described with reference to a proactive malware protectionmethodology implemented within a Microsoft® Windows® kernel mode driver,the present invention is equally applicable to various other operatingsystem environments and other applications in which monitoring and/orenforcement of software activity is desired. For example, according toone embodiment, techniques described herein may be used to monitor andtrack software use activity by logging the execution and use of all orselected types or categories of modules on a computer system or network.Additionally, various of the methodologies described herein may be usedto enforce and monitor floating licenses for software applications bylimiting the number of concurrent users of a particular softwareapplication. Various other usage scenarios, such as copy enforcement,software/application use management, and/or the like, for a system asdescribed herein will be apparent to those of ordinary skill in the art

For the sake of illustration, various embodiments of the presentinvention have herein been described in the context of computerprograms, physical components, and logical interactions within moderncomputer networks. Importantly, while these embodiments describe variousaspects of the invention in relation to modern computer networks andprograms, the method and apparatus described herein are equallyapplicable to other systems, devices, and networks as one skilled in theart will appreciate. As such, the illustrated applications of theembodiments of the present invention are not meant to be limiting, butinstead exemplary. Other systems, devices, and networks to whichembodiments of the present invention are applicable include, but are notlimited to, other types communication and computer devices and systems.More specifically, embodiments are applicable to communication systems,services, and devices such as cell phone networks and compatibledevices. In addition, embodiments are applicable to all levels ofcomputing from the personal computer to large network mainframes andservers as well as being applicable to local area networks (LANs) andwide area networks (WANs), such as enterprise-wide networks.

Terminology

Brief definitions of terms, abbreviations, and phrases used throughoutthis application are given below.

The phrase “code module” generally refers to any file that containsinformation that may be interpreted by a computer system. Examples ofcode modules include executable objects, file system objects, datafiles, text files, script files and/or the like. Furthermore, codemodule objects, such as visual basic scripts, JavaScript, Windows-basedscripts, Java applets, and/or the like, are intended to be encompassedby the phrase “code module.” Common file extensions of executableobjects include, but are not limited to, .exe, .com, .sys, .dll, .scr,.cpl, .api, .drv, .bpl and/or the like. File system objects includeobjects like device drivers, network interfaces, and/or the like. Otherexamples of code modules may include files using the IEEE-695 standard,S-records, PEF/CFM Mach-O (NeXT, Mac OS X), a.out (Unix/Linux), COFF(Unix/Linux), ECOFF (Mips), XCOFF (AIX), ELF (Unix/Linux), Mach-O (NeXT,Mac OS X), Portable Executable, IBM 360 object format, NLM, OMF, SOM(HP), XBE (Xbox executable), and/or the like.

The terms “connected” or “coupled” and related terms are used in anoperational sense and are not necessarily limited to a direct physicalconnection or coupling. Thus, for example, two devices may be coupledirectly, or via one or more intermediary media or devices. As anotherexample, devices may be coupled in such a way that information can bepassed therebetween, while not sharing any physical connection on withanother. Based on the disclosure provided herein, one of ordinary skillin the art will appreciate a variety of ways in which connection orcoupling exists in accordance with the aforementioned definition.

The phrase “content authenticator” generally refers to a result of amethod for generating an authenticating mark which may be used inverifying digital information, files, code and/or data segments of codemodules and/or the like. For example, in some cases a method of contentauthentication comprises two complimentary algorithms. One forgenerating the authenticating mark and one for verifying theauthenticating mark. In one embodiment, a digital signature is employedas the content authenticator. A digital signature or cryptographicdigital signature denotes the result of computing a cryptographic hashvalue, such as a Secure Hash Algorithm (e.g., SHA-1, SHA-256), MessageDigest #5 (MD-5), and the like, over a specific body of encoded data,then encrypting the hash value using a private key. Given the same bodyof encoded data, re-computing the hash value, and decrypting the digitalsignature using the corresponding public key, will produce the identicalvalue if the encoded data remains the same. According to one embodiment,in an effort to increase real-time performance, content authenticatorsmay be generated and validated for only the code segment of a codemodule representing an executable. In other embodiments, the contentauthenticators may cover both the code and data segments of code modulesrepresenting executables.

The phrase “global whitelist” generally refers to a whitelistidentifying commonly accepted code modules that are approved forexecution. In one embodiment, a global whitelist is a list of all knownapproved code modules, not limited to those existing on any oneparticular computer system. According to various embodiments, the globalwhitelist may be provided by a source external to the organization,enterprise or individual end user or group of end users whose codemodules are whitelisted. In some embodiments, a trusted service providermay maintain a global whitelist and allow local copies of the globalwhitelist to be stored on computer systems associated with a registereduser of the trusted service provider. In other embodiments, the globalwhitelist may exist only in one or more protected servers and is notdistributed in the form of local copies. In one embodiment, the globalwhitelist may be populated with a truly “global” list of all known safecode modules as identified by multiple sources. In other embodiments,the global whitelist may be edited and/or created by an administratorbased on an enterprise-, division-, development group-wide softwarepolicy, for example. In addition, according to various embodiments, theglobal whitelist database may be updated on a periodic schedule such asyearly, monthly, weekly, etc. or on an as needed basis. In an enterprisenetwork, for example, the global whitelist database might contain alimited subset of known good code modules that are approved for use withthe particular enterprise. As an example, a global whitelist mayidentify code modules associated with common operating system software,operating system services, and common utilities such as word processors,internet browsers, and/or the like. In addition, a global whitelistdatabase may contain one or more fields that contain various informationabout the code module or the entry in the global whitelist. For example,in some cases the fields may include one or more of the following: acontent authenticator, a file name and/or a file path, informationidentifying the user or process that created and/or last edited theentry, a run option, additional flags describing what processing shouldoccur for this entry such as an “interpreter” flag, a time stamp, and/orthe like. In some embodiments, the run option for a given entry canencode more information and indicate a wider range of processing thanjust allow. Thus, it is understood that “whitelist” as used inaccordance with various embodiments stores more than just the list ofauthenticators that are valid; it should be understood to have thebroader meaning of the list of authenticators for which it is desired toperform some specific processing (e.g., deny, prompt, etc).

The phrases “in one embodiment,” “according to one embodiment,” and thelike generally mean the particular feature, structure, or characteristicfollowing the phrase is included in at least one embodiment of thepresent invention, and may be included in more than one embodiment ofthe present invention. Importantly, such phases do not necessarily referto the same embodiment.

The phrase “local whitelist” generally refers to a whitelist whichidentifies code modules which have been locally approved for executionon one or more computer systems or a whitelist that has otherwise beencustomized for use by one or more particular computer systems. Thelocal/global qualifier when used in connection with the term whitelistdoes not necessarily refer to where the whitelist is stored, but ratheris intended to refer to the size, scope or quantity of entries in thewhitelist. Typically, a global whitelist would be expected to be morecomprehensive than a local whitelist. In one embodiment, the localwhitelist may be stored in a memory store. In contrast to globalwhitelists, a local whitelist allows for a more specific customizationof the computer software which may be run on an individual computer,thereby allowing an administrator to tailor a local whitelist to allowor disallow particular code modules. According to various embodiments, alocal whitelist database may contain entries for files known to beinstalled on one or more computer systems. For example, according tosome embodiments, a local whitelist may be created by a computer lockdown procedure that scans one or more local computers for code moduleswhich are then added to the local whitelist database. In otherembodiments, an end user or administrator may be authorized to add orremove entries indicating which code modules are allowed to executeand/or load. The entries found within a local whitelist, according tosome embodiments, may consist of a content authenticator value, filename and/or file path information, run-options and flags. Flags cancontain information, such as whether the corresponding code module is ascript interpreter, or whether the code module is being monitored by afloating license server. In each case, it should be understood that theterms local whitelist and global whitelist do not necessarily implyseparate file storage. Indeed, the local and global entries, at leastaccording to some embodiments, could all be stored in a single file withan appropriate flag on each entry indicating its local/global status.Such statuses are important for being able to properly update thelocally stored lists from external sources.

If the specification states a component or feature “may”, “can”,“could”, or “might” be included or have a characteristic, thatparticular component or feature is not required to be included or havethe characteristic.

The phrases “memory store” or “data store” generally refer to anydevice, mechanism, or populated data structure used for storinginformation. For purposes of this patent application, “memory store” or“data store” are intended to encompass, but are not limited to, one ormore databases, one or more tables, one or more files, volatile memory,nonvolatile memory and dynamic memory. By way of further illustration,for example, random access memory, memory storage devices, and otherrecording media are covered by the phrase “memory store” or “datastore.” Common examples of a memory store include, but are not limitedto, magnetic media such as floppy disks, magnetic tapes, hard drivesand/or the like. Other examples of “memory stores” include SIMMs, SDRAM,DIMMs, RDRAM, DDR RAM, SODIMMS, optical memory devices such as compactdisks, DVDs, and/or the like. In addition, a “memory store” may includeone or more disk drives, flash drives, databases, local cache memories,processor cache memories, relational databases, flat databases, and/orthe like. This list is no way meant to be an exhaustive list of devicesand/or data structures falling with in the definition of “memory store,”but is instead meant to highlight some examples. Those skilled in theart will appreciate many additional devices and techniques for storinginformation which are intended to be included within the phrase “memorystore.”

The phrase “MRU cache” or “most recently used cache” generally refers toa most recently used list of code modules that have been requested orthemselves have requested to be loaded or mapped into memory or tocreate a process. In one embodiment, the MRU cache is used toefficiently identify authorized and/or unauthorized code modules withouthaving to recalculate a content authenticator associated with the codemodules as the code module has relatively recently already beenauthenticated. Accordingly, new entries may be added to the MRU cache ascode modules are authenticated and then allowed or disallowed to load orexecute. In some embodiments, the MRU cache is an in-memory list of codemodule file path names (identifying EXEs, DLLs, Scripts, etc.) andassociated run-options for the corresponding file path names. Accordingto various embodiments, the MRU cache may be updated when a kernel-leveldriver intercepts file system write activity for any of the filesidentified in the MRU cache. As such, the cache entry for the particularfile may be removed from the list or otherwise invalidated to preclude afile that may have been modified by being authenticated based on the MRUcache. Other embodiments provide for the MRU cache may be stored in anymemory store. The use of a MRU cache may provide a significantperformance enhancement by allowing the kernel-level driver to bypassthe steps of having to calculate and look up the content authenticatorassociated with the code module in one or more of the higher-levelwhitelists each time a code module is loaded into memory.

The phrase “multi-level whitelist” general refers to a whitelistarchitecture in which a hierarchical whitelist approach with multiplewhitelists of varying scope and/or an MRU cache are employed.Accordingly, a priority is created that governs the order in which thewhitelists and caches are checked. Some embodiments of a multi-levelwhitelist may use one or more of MRU caches, one or more local whitelistdatabases, and/or one or more global whitelist databases.

The term “responsive” includes completely or partially responsive.

The phrase “run options” generally refers to an indicator associatedwith one or more code modules of whether a code module should beunconditionally allowed to execute, unconditionally denied to execute,or if more information is required before a decision can be made aboutthe execution of the code module. In some embodiments, a run option mayindicate that a license check is required, administrator approval isrequired, that the code module may be allowed if certain conditions aremet, or that the code module should be disallowed under certainconditions. For example, a music player or instant message applicationmay be associated with a run option that will only allow execution ofthe code modules after work hours.

The term “whitelist” generally refers to an access control mechanismthat may identify a set of one or more code modules approved forexecution on one or more computer systems. In some embodiments, awhitelist may also include information identifying a set of one or morecode modules that are not approved for execution (e.g., blacklistinformation). A whitelist may be stored in a memory store or a datastore resident in local memory, on a mass storage device, on a remotemachine or distributed across one or more remote machines. In someembodiments, a whitelist may also contain information associated withthe code modules, such as a file name or file path (e.g., a file nameand/or associated extension or a fully qualified path of a file),content authenticator, special file tags, known associations, and/or thelike.

Exemplary System Overview

FIG. 1 is a high level architectural diagram of a multi-level whitelistauthentication system 100 for allowing the execution of authorizedcomputer code in accordance with one embodiment of the presentinvention. According to the present example, the multi-level whitelistauthentication system 100 includes a user interface layer 105, a usermode service layer 110 and a kernel mode driver 160.

In one embodiment, the kernel mode driver 115 interacts with and makesuse of various other components, such as an OS file system activitymonitor 155, an OS process creation monitor 150, an OS module loadactivity monitor 145 and a local whitelist 135, to perform real-timeauthentication of code modules. According to one embodiment, the OS filesystem activity monitor 155 may also be configured to monitor andprotect one or more of the whitelists such as MRU cache 160, localwhitelist 135, and/or global whitelist 130. In one embodiment, thekernel mode driver 115 hooks low level operating system APIs tointercept various OS operations, such as process creation, moduleloading, and file system input/output (I/O) activity. In this manner,the kernel mode driver 115 may perform appropriate authenticationprocessing prior to the loading or mapping of a requested code moduleinto memory or prior to the execution of a requested code module.

According to the present example and as will be described in furtherdetail below, during the creation of any new processes, or the loadingof a code module by an existing process, the kernel mode driver 115 canmake a determination as to whether to allow the particular operation tocontinue (e.g., grant the request) or deny the request (e.g., bypropagating an error code to the user mode service layer 110) withreference to an MRU cache 160 and the local whitelist 135.

According to one embodiment, the local whitelist 135 contains entriesfor files known to be resident on the local computer system or withinthe LAN or enterprise network. The local whitelist 135 may be stored inRAM or in a disk file. As described further below, in one embodiment,entries of the local whitelist 135 include a content authenticatorvalue, path information, run-options and flags associated with each codemodule. Flags can contain information such as whether the correspondingcode module is a script interpreter or whether the code module is beingmonitored by a floating license server, such as floating license server120. As described further below, in accordance with a typicalauthentication scenario that does not include the optional cacheacceleration technique (described below), responsive to a request toexecute or load a code module, the multi-level whitelist authenticationsystem 100 first attempts to authenticate the code module with referenceto the local whitelist 135 (e.g., calculate a content authenticatorvalue associated with the code module and compare the calculated valueto the expected value stored in the local whitelist 135). If suchauthentication is inconclusive, then authentication processing continueswith reference to the global white list 130.

As described further below, a cache acceleration technique involving theuse of an optional most recently used (MRU) cache 160 facilitatesreal-time authentication of code modules by maintaining a relativelysmall set of cache entries relating to code modules that have recentlybeen requested to execute, such as executables, dynamically-linkedlibraries (DLLs) and scripts. When employed, the MRU cache 160 providessignificant performance enhancement by allowing the kernel mode driver115 not to have to calculate and look up the content authenticator eachtime a commonly used code module is loaded.

According to one embodiment, the MRU cache 160 is an in-memory list ofpath names and associated run-options for the most recently requestedcode modules. Entries may be added to the MRU cache 160 after codemodules are authenticated by other means (e.g., with reference to thelocal whitelist 135, the global whitelist 130, or after explicitapproval by the end user or the system or network administrator). Sincecode modules identified by entries of the MRU cache 160 have alreadybeen recently authenticated, as long as the file associated with codemodule remains unaltered, there is no need to perform the time consumingprocess of calculating and looking up the content authenticator for therequested code module.

According to one embodiment and as described in further detail below,the kernel mode driver 115 protects the integrity of the MRU cache 160by removing or otherwise invalidating cache entries associated withfiles that may have been altered. For example, when the kernel modedriver 115 intercepts file system write activity via the OS file systemactivity monitor 155 for any of the files in the MRU cache 160, theentry associated with the file may be removed from the list or marked asinvalid to allow subsequent cache processing to overwrite the entry.Consequently, in one embodiment, if a valid entry associated with therequested code module is found in MRU cache 160, then an acceleratedauthentication of the requested code module may be performed by simplyusing the previous authentication results.

The global whitelist 130 is a list of approved code modules that is notlimited to those existing on a particular computer system. According toone embodiment, the global whitelist 130 is an externally suppliedknowledge base of known safe software modules that may be gathered fromone or more sources. While in some implementations, the global whitelist130 may be populated with a truly “global” list of all known safesoftware, it is contemplated that within an enterprise network, theglobal whitelist 130 might contain only a limited subset of known goodsoftware that is approved for use with the particular enterprise. In oneembodiment, the global whitelist 130 contains the same fields as thelocal whitelist 135.

According to one embodiment, the user mode service layer 110 providesservices that help make decisions about whether to allow execution ofcode modules that the kernel mode driver 115 cannot affirmativelyauthenticate. For example, if the kernel mode driver 115 cannot locatean entry for a code module in either the MRU cache 160 or the localwhitelist 135, then responsibility for completing authentication of thecode module may propagate up the chain to the user mode service layer110. In the present example, configuration options 140 stored within theuser mode service layer 110 may help determine the actions that aretaken in these cases. For example, the configuration options 140 mayinclude such items as whether the end user or a system or networkadministrator should be prompted to allow unknown code modules toexecute (permissions), whether a Global Whitelist Server should becontacted to obtain approval, whether the floating license server 120should be contacted to obtain approval, etc. In one embodiment, the usermode service layer 110 may also be responsible for logging (storing)information about the operation of the system, etc.

In the present example, the user interface layer 105 is responsible fordisplaying information to the end user of the computer system and/or fordisplaying information to a system or network administrator. This mayinclude prompting the end user or administrator for permission toexecute an unknown code module (if the configuration options 140 are setto do that) or simply notifying the user and/or administrator that acode module was denied execution as a result of the operation of themulti-level whitelist authentication system 100.

A global whitelist server 125 may be a server to which the multi-levelwhitelist authentication system 100 is connected over the Internet or itmay be a locally hosted server in an enterprise network. In oneembodiment, the global whitelist server 125 is an external source forreceiving updated whitelist information. Depending upon the particularimplementation, the global whitelist server 125 may allow a completelocal copy to be stored with the multi-level whitelist authenticationsystem 100 or the global whitelist server 125 may simply respond toindividual code module information queries.

In embodiments in which it is desirable to enforce concurrent instancelimitations on particular software applications, a floating licenseserver 120 may be included to centrally manage the number of concurrentexecutions of particular code modules. According to one embodiment, thefloating license server 120 may be programmed to allow a limited numberof concurrent executions for certain modules. For example, when amonitored application is launched, the available license count may bedecremented. When that instance of the application terminates, thefloating license server 120 is notified so that it can increment theavailable license count.

As described further below, in one embodiment, the floating licenseserver 120 may be queried by individual clients to determine whetherlicenses are available at a given time to execute the monitoredapplication(s). If there is not an available license when one isrequested, it will return that information so that the client can denythe execution at that time. Advantageously, in this manner, anapplication that is not otherwise provided with built in capabilities toperform license enforcement may be subjected to concurrent executionlimitations as may be desired by an enterprise or otherwisecontractually imposed by an application provider, for example.

In the present example, a Remote Signing Server (RSS) 165, may be usedto protect one or more of the global whitelist 130, the local whitelist135 and the MRU cache 160 with an externally generated digitalsignature. The digital signature may be based in part upon a hash valuefor the data in the corresponding whitelist. This signature may then beencrypted remotely by a Remote Signing Server (RSS) using private keyencryption. Then, each time one or more of the whitelists are read intomemory to look up a value during normal operation, the hash value may berecalculated by the authentication system software, and compared to theunencrypted stored value (unencrypted using the public key). If the twohash values compare equally, then it can be reasonably assured that theauthenticated whitelist has not been modified maliciously.

Some embodiments additionally provide for a client verification schemeaccording to which a caller of the RSS 165 is confirmed to be anauthorized code module associated with the authentication systemsoftware by requiring the caller to provide identifying information,such as a machine ID, a password, and/or the like.

In one embodiment, the client verification scheme employs an un-storedpassword (from user memory) that is used when an end-user installs theauthentication system software and creates a new account on the RSS,he/she may be prompted to provide a password or phrase to the serverthrough a web page that is never stored on the end user system. The usermay then be asked to provide this password during the database signingprotocol.

In addition, some embodiments provide for abuse/misuse detection.According to one embodiment, the RSS contains code to monitor requestsmade of it and looks for patterns of malicious use, such as repeatedfailed authentications from the same IP address, etc.

Exemplary Computer System Overview

Embodiments of the present invention include various steps, which willbe described in more detail below. A variety of these steps may beperformed by hardware components or may be embodied inmachine-executable instructions, which may be used to cause ageneral-purpose or special-purpose processor programmed with theinstructions to perform the steps. Alternatively, the steps may beperformed by a combination of hardware, software, and/or firmware. Assuch, FIG. 2 is an example of a computer system 200, such as aworkstation, personal computer, client, or server, upon whichembodiments of the present invention may be utilized.

According to the present example, the computer system includes a bus201, at least one processor 202, at least one communication port 203, amain memory 204, a removable storage media 205 a read only memory 206,and a mass storage 207.

Processor(s) 202 can be any know processor, such as, but not limited to,an Intel® Itanium® or Itanium 2® processor(s), or AMD® Opteron® orAthlon MP® processor(s), or Motorola® lines of processors. Communicationport(s) 203 can be any of an RS-232 port for use with a modem baseddialup connection, a 10/100 Ethernet port, or a Gigabit port usingcopper or fiber. Communication port(s) 203 may be chosen depending on anetwork such a Local Area Network (LAN), Wide Area Network (WAN), or anynetwork to which the computer system 200 connects.

Main memory 204 can be Random Access Memory (RAM), or any other dynamicstorage device(s) commonly known in the art. Read only memory 206 can beany static storage device(s) such as Programmable Read Only Memory(PROM) chips for storing static information such as instructions forprocessor 202.

Mass storage 207 can be used to store information and instructions. Forexample, hard disks such as the Adaptec® family of SCSI drives, anoptical disc, an array of disks such as RAID, such as the Adaptec familyof RAID drives, or any other mass storage devices may be used.

Bus 201 communicatively couples processor(s) 202 with the other memory,storage and communication blocks. Bus 201 can be a PCI/PCI-X or SCSIbased system bus depending on the storage devices used.

Removable storage media 205 can be any kind of external hard-drives,floppy drives, IOMEGA® Zip Drives, Compact Disc-Read Only Memory(CD-ROM), Compact Disc-Re-Writable (CD-RW), Digital Video Disk-Read OnlyMemory (DVD-ROM).

The components described above are meant to exemplify some types ofpossibilities. In no way should the aforementioned examples limit thescope of the invention, as they are only exemplary embodiments.

FIG. 3 is a flow diagram illustrating an exemplary method 300 for newprocess creation authorization processing in accordance with oneembodiment of the present invention. In accordance with the presentexample, a monitoring step, step 310, monitors for process creationrequests from code modules. In one embodiment, the kernel mode driver115 is activated as new processes are created, just before execution.For example, in the context of the Windows operating system, the OSprocess creation activity monitor 150 may intercept new process creationactivity by hooking to the Windows CreateSection API call and inresponse temporarily turning control over to the kernel mode driver 115to allow appropriate authentication processing to be performed. Themonitoring for new process creation requests may occur during systemboot processing or during normal system operations.

At decision block 320, a determination may then be made as to whetherthe code module is authorized to execute. According to one embodiment, amulti-level whitelisting approach may be used. One embodiment of themulti-level whitelisting approach is described in more detail withreference to FIG. 6. Briefly, in accordance with one embodiment, acontent authenticator of the code module being loaded may be calculatedand compared to the expected value stored in an entry of one or more ofthe multiple whitelists available. If the entry is found, theauthorization determination may based on one or more parameters as towhether the request should be approved; and then control is returned tothe operating system. In one embodiment, requests may be unconditionallyapproved, unconditionally denied, or a decision may need to be made byan authorized user.

If the request is granted, control flow continues along the “Yes” pathexiting decision block 320 to block 345. If the request is denied,control flow continues along the “No” path from decision block 320 toblock 330. Otherwise, if no determination can be made without furtherinput from an authorized user, for example, then the determination maybe unknown and control flow continues along the “UnK” path from decisionblock 320 to block 355.

At block 345, a decision has previously been made that the code modulein question may continue to load and execute in the normal fashion. Inone embodiment, this means that the code module is granted access tosystem resources such as memory, processors, and/or the like.

At block 330, a decision has previously been made that the code modulein question is not allowed to create a new process and the new processcreation request is denied. As described in more detail below, a denialmay arise for multiple reasons. For example, in one embodiment, a runoption may be set to an “unconditional deny” state in one or more of thewhitelists. Once this is found, according to various embodiments, therequest may be denied and access will not be granted to the systemresources such as memory, processors, and the like. In otherembodiments, a request may be denied if there are not enough licenses toallow another concurrent instance of a particular software application,for example, that is subject to monitoring by a floating license server.Still yet in other cases, the denial may occur based on one or moreconditions placed on the code module for execution. For example, awhitelist may indicate that a code module may be executed only during acertain period of the day. As such, if it is not during the time periodindicated, then denial relating to the creation of a new processassociated with the requested code module may occur. As another example,a whitelist may indicate that only certain users are authorized toexecute a particular code module. As such, when another user attempts toexecute the code module, the request may be denied.

In one embodiment, if a new process creation request is denied orgranted, information associated with the denial or allowance may berecorded at blocks 335 and 350, respectively. Various additionalinformation associated with the denial or allowance may be recorded. Forexample, parameters such as a time stamp, reason for denial/allowance,such as run option set to unconditional deny/allow, whitelist level atwhich the determination was made, whether the denial/allowance was as aresult of user input, the content authenticator calculated for the codemodule, code module name, code module file path, machine id, and/or thelike. In various embodiments, this information may be stored in one ormore databases. In other embodiments, the information may be transmittedto an external monitoring system which may prepare a summary ofdenied/allowed process creation requests. This report may then betransmitted to a designated person on a periodic or on-demand basis. Atblock 340, in some embodiments, in addition to or instead of recordinginformation associated with the process creation denial, an error codeassociated with the process creation denial may be displayed to an enduser, system administrator or other authorized personnel.

According to one embodiment, the information associated with the denialof the new process creation request may be used to remove theunauthorized code modules from the system. This may be doneautomatically, using manual user intervention, and/or a combination ofthe two. For example, if the code module associated with the new processcreation request is known malware, the code module may be automaticallyremoved. In other cases, user intervention may be desirable. In othercases, nothing may need to be done immediately. For example, if thereason for unconditional denial is because there are not enough licensescurrently available, then no further action is necessary. However, insome embodiments, information associated with a denial based oninsufficient licenses may be used to determine if additional licensesmay need to be purchased.

At block 355, a decision has previously been made that the code moduleauthorization processing of block 320 resulted in an “unknown” state,e.g., there is a need for more information or intervention on the partof an authorized user. According to one embodiment, when this occurs, arequest may be made at block 355 for an administrator or end user todetermine whether the new process creation request should be granted.For example, when a request is received from a code module that may havea legitimate purpose, but is either not currently in one or more of thewhitelists or is currently in one or more of the whitelists but isassociated with a run option of “additional authorization required,” forexample, then a decision may be requested from an administrator or enduser. An administrator may use behavior analysis techniques, such assandboxing, to determine if such code module requests should be granted.In accordance with various embodiments, it should be understood thatthis appeal to additional authority includes but is not limited to:real-time notification of an administrator or querying one or moreexternal servers that might have more knowledge about the approvalstatus of this module.

According to one embodiment, one or more options may be presented to theend user when a request for a decision is made. In some cases, theoptions presented may depend on whether the new process creation requestoccurred during a boot process or after the system is fully booted. Inother cases, special configuration options control behavior of thesystem before a user or management console control is available from theoperating system. For example, a user prompt, unattended deny and logmode, and/or a user self-lockdown mode may be present in one or moreembodiments of the present invention. According to one embodiment, theuser may be prompted that an unapproved module is attempting to executeand may be given various options from which to select. According to oneembodiment, the user may be given the following choices: (1) allow thecode module to execute this time, but continue to warn or prompt onsubsequent attempts (no modification of any whitelists takes place); (2)deny this code module from executing this time and prompt on subsequentattempts (again, no whitelist modification takes place); (3) allow thiscode module to execute this time and in the future—add an entry in alocal whitelist; and/or (4) deny this code module from executing thistime and in the future—set run option in one or more of the availablewhitelists to unconditional deny.

According to one embodiment, in the unattended deny and log mode, thesystem will deny execution of all unapproved code modules. According tosome embodiments, even code modules which have an unknown determinationmay be denied. In some embodiments, a log file entry may be made notingthat the unapproved code module attempted to execute. No usernotification or interaction is required. This may be useful in the caseof server, for example, since a servers normally do not have an end userimmediately available.

If the user self-lockdown mode is active, various embodiments providethat the user may elect to deny all unapproved code modules, but benotified when one attempts to execute through the user interface. Insome embodiments, this may be an immediate notification such as a pop-updialog screen, audible notification, print out, e-mail, and/or the like.Other embodiments provide for notification on an on-demand basis or aperiodic basis, such as hourly, daily, weekly, and the like.

FIG. 4 is a flow diagram illustrating a method 400 for authorization ofloading of code modules by running processes in accordance with oneembodiment of the present invention. In accordance with the presentexample, a monitoring step, step 410, monitors for the loading of codemodules by running processes. In one embodiment, the kernel mode driver115 is activated as module load activity occurs. For example, in thecontext of the Windows operating system, the OS module load activitymonitor 145 may intercept module loading activity by hooking to theWindows CreateSection API call and in response thereto temporarilyturning control over to the kernel mode driver 115 to allow appropriateauthentication processing to be performed.

Once a request from a running process is received to load a code module,such as a .dll, .exe, script file, and/or the like, a determination ismade at decision block 320, as to whether the request should beauthorized. According to various embodiments, a multi-level whitelistingapproach may be used. A more detailed description of how this decisionis made in accordance with one embodiment of the present invention isprovided below. Briefly, in accordance with one embodiment, decisionblock 320 may result in an unconditional deny, an unconditional allow,or an unknown state (in which case, a decision may be solicited from anauthorized user).

According to one embodiment the determination made by decision block 320may involve determining the name of the code module attempting to beloaded and/or associating the code module attempting to be loaded withthe code module or process that made the request. Notably, while therunning code module making this request to further load an additionalcode module (the dependent code module) has already been approved torun, it is not necessarily the case that all dependent code modulesrequested to be loaded by the running code module should be allowed. Forexample, a script interpreter may be allowed to run, but it may not beallowed to load a known malicious script file. Additionally, an Internetbrowser may be allowed to run, but it may not be allowed to run certainplugins or scripts. As such, in one embodiment, the determination withrespect to allowing or disallowing the loading of a dependent codemodule, may be conditional upon the source of the load request (e.g.,the identity, hash value and/or type of the code module associated withthe running process that initiated the load request) and/or upon thehash value of the dependent code module.

If the request is granted, control flow continues along the “Yes” pathexiting decision block 320 to block 445. If the request is denied,control flow continues along the “No” path from decision block 320 toblock 430. Otherwise, if no determination can be made without furtherinput from an authorized user, for example, then the determination maybe unknown and control flow continues along the “UnK” path from decisionblock 320 to block 455.

At block 445, a decision has previously been made that the code modulein question may continue to be mapped into memory. In one embodiment,this means that the code module is granted access to system resourcessuch as memory, processors, and/or the like. In some cases, thedetermination as to whether the load request should be granted maydepend on the running process which is performing the loading request.For example, some running processes may be authorized to load certaincode modules, while other running processes may not be allowed to loadthe same code modules. If the source of the load request is a scriptinterpreter, for example, then the dependent code module may beauthenticated with reference to a multilevel whitelist architecture;however, if the source of the load request is a text editor, forexample, then authentication of the dependent code module may bebypassed as there is no intent to run the script.

At block 430, a decision has previously been made that the code modulein question is not allowed to be mapped into memory and that the codemodule load request is denied. As described in more detail below, adenial may arise for multiple reasons. For example, in one embodiment, arun option may be set to an “unconditional deny” state in one or more ofthe whitelists. Once this is found, according to various embodiments,the request may be denied and access will not be granted to the systemresources such as memory, processors, and the like. In otherembodiments, the denial may occur based on conditions placed on the codemodule for loading, such as those discussed above with reference to FIG.3.

In some embodiments, if a load module request is denied or granted,information associated with the denial or allowance may be recorded, seeblocks 435 and 450. Various information associated with thisunconditional denial or unconditional allowance may be recorded atblocks 435 and 450, respectively. For example, parameters such as a timestamp, reason for denial/allowance, such as run option set tounconditional deny/allow, the running process requesting the loading ofthe code module, whitelist level at which the determination was made, ifthe denial/allowance resulted from user input, the content authenticatorcalculated for the code module, code module name, code module file path,machine id, and/or the like.

In various embodiments, this information may be stored in one or moredatabases. In other embodiments, the information may be transmitted toan external monitoring system which may prepare a summary ofdenied/allowed code module load requests. As indicated above, withreference to FIG. 3, such a report may then be transmitted to adesignated person on a periodic or on-demand basis. Other embodiments,simply determine an error code when the load code module request isdenied and transmits this error code to an end user, systemadministrator or other authorized personnel, see step 440.

At block 455, a decision has previously been made that the code moduleload authorization processing of block 320 resulted in “unknown” state,e.g., there is a need for more information or intervention on the partof an authorized user. According to one embodiment, when this occurs, arequest may be made at block 455 for an administrator or end user todetermine whether the load request should be granted. Variousembodiments allow for different options. As such, it should beunderstood that this appeal to additional authority includes but neednot be limited to real-time notification of an administrator or queryingone or more external servers that might have more knowledge about theapproval status of this module.

According to one embodiment, one or more options may be presented to theend user when a request for a decision is made. In some cases, theoptions presented may depend on whether the loading request occurredduring a boot process or after the system is fully booted. As describedabove with reference to FIG. 3, in other embodiments, specialconfiguration options may control behavior of the system before a useror management console control is available from the operating system.For example, a user prompt mode, unattended deny and log mode, and/or auser self-lockdown mode may be supported in accordance with oneembodiment. According to one embodiment, in user prompt mode, the usermay be provided with one or more of the following choices: (1) allowthis code module to be mapped into memory this time, but continue towarn or prompt on subsequent attempts (no modification of multi-levelwhitelists); (2) deny this code module from being mapped into memorythis time and prompt if it attempts to do so in the future (nomulti-level whitelist modification); (3) allow this module to be mappedinto memory this time and in the future—add a content authenticator to awhitelist; and/or (4) deny this code module from being mapped intomemory this time and in the future—set run option to unconditional denyin the whitelist.

FIG. 5 conceptually illustrates an exemplary multi-level whitelistdatabase system 500 in accordance with one embodiment of the presentinvention. According to one embodiment, multiple whitelists with varyingscope may be used to authenticate requests. In the present example, anMRU cache 505, a local whitelist 520, and a global whitelist 550 areconsulted to authenticate requests. In one embodiment, there may be oneor more of each scope/level of whitelist. In other embodiments, one ormore levels of whitelist may not be present.

According to one embodiment, authentication processing of a requestrelating to a code module begins with the MRU cache 505, if insufficientinformation exists in the MRU cache 505 to make a deny/grant decision,then authentication processing continues with the one or more localwhitelists 520. If insufficient information exists in the one or morelocal whitelists 520, then authentication processing continues withreference to either the floating license server 545 or the one or moreglobal whitelists 550. If insufficient information exists in the one ormore global whitelists 550, then the decision regarding whether to allowor deny loading or execution of the code module in question may bedelegated to an authorized user 555.

The MRU cache 505 allows the use of a cache acceleration techniqueinvolving the use of an optional most recently used list. The MRU cache505 facilitates real-time authentication of code modules by maintaininga relatively small set of cache entries 506 relating to code modulesthat have recently been requested to be executed or to be loaded. Inaddition, these entries generally contain a subset of the informationavailable for the same entries in one or more local whitelists 520and/or one or more global whitelists 550.

Examples of code modules include, but need not be limited to,executables, dynamically-linked libraries (DLLs), scripts, and/or thelike. In one embodiment, the MRU cache 505 may be stored in locally inmemory, in a swap file, and/or the like. In other embodiments, the MRUcache 505 may be stored on other storage media locally, or in somecases, even remotely.

According to one embodiment, the MRU cache 505 comprises an in-memorylist of entries 506 identifying path names 510 and previously associatedrun-options 515 for the most recently requested code modules. Entriesmay be added to the MRU cache 505 after code modules are authenticatedby other means.

A second tier of the multi-level whitelist approach may include one ormore local whitelists 520. A local whitelist generally would be expectedto be more comprehensive than an MRU cache and less comprehensive than aglobal whitelist. According to one embodiment, a local whitelist mayidentify code modules which have been locally approved for execution onone or more computer systems or a whitelist that has otherwise beencustomized for use by one or more particular computer systems. Accordingto various embodiments, a local whitelist database 520 may containentries 521 for files known to be installed on one or more computersystem. For example, according to one embodiment, a local whitelist maybe created by a computer lock down procedure that scans one or morelocal computers for code modules which are then added to the localwhitelist database 520. In other embodiments, an end user oradministrator may be authorized to add or remove entries indicatingwhich code modules are allowed to execute and/or load.

In one embodiment, the entries 521 found within the local whitelist 520may consist of a file path 525, content authenticator value 530,run-options 535 and administrative information 540. Run-options 535 mayconsist of one or more of the following states: “unconditional allow,”“unconditional deny,” “conditional allow based on flags,” or “requiresadditional user authorization.” In one embodiment, the local whitelist520 may contain flags indicating information, such as whether thecorresponding code module is a script interpreter and conditions onexecution. For example, in one embodiment, a condition on execution maybe approval from the floating license server 545. In another embodiment,compliance with time prohibitions or time authorizations may benecessary for the code module to be loaded or executed. For example, acorporate enterprise may only allow the execution of code modulesassociated with non-work-related software applications, such as a musicplayer application, after regular business hours.

If an entry contains a flag indicating that the code module is beingmonitored by a floating license server 545, the compliance withrestrictions placed by the floating license server will be necessary forthe code module to execute. For example, only a limited number alicenses may be available for concurrent instances of a particular codemodule. In this case, there must be a free license before the codemodule will be allowed to execute. As another example, within acorporate setting, a license may only be valid for a particular physicalsite or location, a particular computer, or by a particular user or setof users. In these cases, compliance with these license restrictionsmust be met before the code module will be allowed to execute.

Some embodiments, allow for the use of one or more global whitelists550. Typically, a global whitelist would be expected to be morecomprehensive than a local whitelist. A global whitelist 550 mayidentify commonly accepted code modules that are approved for execution.In one embodiment, the global whitelist 550 represents a list of allknown approved code modules, not limited to those existing on any oneparticular computer system or those within a particular corporateenterprise.

In some embodiments, the global whitelist 550 may identify code modulesassociated with common operating system software, operating systemservices, and common utilities such as word processors, internetbrowsers, and/or the like. In addition, entries 551 of the globalwhitelist database 550 may contain one or more fields that containvarious information about the corresponding code module. For example, insome cases the fields may include the same fields as described inconnection with the local whitelist 520. In other cases, a globalwhitelist may contain additional information in the entries 551. Forexample, entries 551 in the global whitelist database 550 may containone or more of the following: a file name and/or a file path, a contentauthenticator, information identifying the user or process that createdand/or last edited the entry, a run option, a time stamp, and/or thelike.

As described earlier, according to various embodiments, the globalwhitelist 550 may be provided by a source external to the organization,enterprise or individual end user or group of end users whose codemodules are whitelisted. In some embodiments, a trusted service providermay maintain the global whitelist 550 and allow local copies of theglobal whitelist to be stored on computer systems associated with aregistered user of the trusted service provider. In other embodiments,the global whitelist may exist only on one or more protected servers andis not distributed in the form of local copies. In one embodiment, theglobal whitelist may be populated with a truly “global” list of allknown safe code modules as identified by multiple sources.

In other embodiments, the global whitelist may be edited and/or createdby an administrator based on an enterprise-, division-, developmentgroup-wide software policy, for example. In addition, according tovarious embodiments, the global whitelist database may be updated on aperiodic schedule such as yearly, monthly, weekly, etc. or on an asneeded basis. In an enterprise network, for example, the globalwhitelist database might contain a limited subset of known good codemodules that are approved for use with the particular enterprise.

According to some embodiments, a fourth tier for authenticationprocessing involving prompting an administrator or end user 555 forinstructions regarding whether to allow or disallow the loading orexecution of the code module in question may be included in themulti-level whitelist approach. The prompting for end-user instructionsmay occur after a search in any one of the other levels. Further detailregarding exemplary multi-level code module authorization is providedwith reference to FIG. 6.

FIG. 6 is a flow diagram illustrating a method 600 of using amulti-level whitelist approach in accordance one embodiment of thepresent invention. In accordance with the present example, multiplewhitelists, such as one or more MRU caches, one or more localwhitelists, and one or more global whitelists, may be used toauthenticate requests relating to code modules. In accordance with oneembodiment, available whitelists are prioritized to create a searchorder. In some embodiments, this may be done based on the relativecomprehensiveness or scope of the whitelists. In other embodiments, theorder in which the whitelists are searched may depend on flagsassociated with the code module. Still yet, in other embodiments, theprioritization may be based on the code module extension such as .dll or.exe.

A request for code module authorization may occur in a variety ofmanners, see blocks 310 and 410 of FIG. 3 and FIG. 4, respectively, fortwo examples. In any event, once a request for authorization isreceived, and a prioritization of the available whitelists has beenestablished, the multi-level code module authorization process maybegin.

At block 605, the MRU cache is scanned to determine, see decision block610, if an entry associated with the requested code module is present.If an entry is not found then a content authenticator is computed forthe requested code module at block 615. After the content authenticatorfor the code module is determined, at block 620, the next whitelist ischecked for a matching entry. This whitelist may be another MRU cache, alocal whitelist, or a global whitelist. If no matching entry is found,then at block 630, the next prioritized whitelist is checked. If nomatching entry is found, then a determination is made at decision block640 as to whether there are any more whitelists to search. If not,according to one embodiment, a new entry is created in the lastavailable whitelist level for the code module with the run option set tounknown.

If during decision steps 610, 625, or 635 a entry corresponding to thecode module is found, then processing proceeds to block 650. At block650, a new MRU entry is created (or a least recently used MRU entry isoverwritten) for the code module and the filename and run option foundin the whitelist entry may be recorded in the new MRU entry.

At decision block 653, a determination is made regarding whether tocheck various other flags that may be associated with the whitelistentry. For example, if the run option was already determined to be“deny,” then no further checking need be performed and the run optionmay simply be returned at block 670. Otherwise, however, if the runoption was previously determined to be “allow,” then various other flagsassociated with the whitelist entry may be checked at blocks 655 and665, respectively, to determine whether special scrip file processing orlicense restriction compliance needs to be performed.

At decision block 655, a determination is made based on various flagsthat may be associated with the whitelist entry regarding whether thecode module is a script interpreter. If not, then the run option isreturned at block 670. Otherwise, if the code module is a scriptinterpreter, then at block 660, information about the associated scriptis extracted. For example, information regarding one or more commandline parameters or arguments may be obtained, such as a file path of ascript file to be run by the script interpreter. Then, at block 665, themulti-level code module authorization is performed on the script file.Advantageously, this allows script files to be selectively authorizedfor execution on a computer system in a manner similar to executablefiles. Otherwise, if the run option does not identify the code module asa script interpreter, then processing branches from decision block 655to decision block 665.

At decision block 665, a determination is made based on various flagsthat may be associated with the whitelist entry regarding whether thecode module is one that requires compliance with one or more licenserestrictions, such as the code module being monitored by a floatinglicense server. If so, then at block 680, information regarding thenumber of authorized software licenses is retrieved. Subsequently, atdecision block 685, it is determined whether there is at least one freelicense for the code module to allow an additional concurrent instanceof the code module. If so, then the run option is returned at block 670.If no free licenses are available, then the run option of “deny” isreturned at block 670. In alternative embodiments, additional checks maybe performed, such as whether the user authorized to run this software,whether the request in compliance with physical location restrictions,and/or the like.

Once a run option is returned to the return run option block 670, therun option decision block 690 returns the appropriate result indicatingthe code module is either allowed, denied, or that more information ormanual intervention is required to make the determination.

In conclusion, the present invention provides novel systems, methods andarrangements for securing a computer system by allowing only theexecution of authorized computer program code. While detaileddescriptions of one or more embodiments of the invention have been givenabove, various alternatives, modifications, and equivalents will beapparent to those skilled in the art without varying from the spirit ofthe invention. Therefore, the above description should not be taken aslimiting the scope of the invention, which is defined by the appendedclaims.

What is claimed is:
 1. A method comprising: intercepting, by a kernelmode driver of a computer system, file system or operating systemactivity relating to a code module; selectively authorizing, by thekernel mode driver, the code module by authenticating a contentauthenticator of the code module with reference to a multi-levelwhitelist, the multi-level whitelist comprising (i) a global whitelistdatabase remote from the computer system, the global whitelist databasecontaining content authenticators of approved code modules that areknown not to contain viruses or malicious code and (ii) a localwhitelist database containing content authenticators of at least asubset of the approved code modules; allowing the file system oroperating system activity relating to the code module when the contentauthenticator matches one of the content authenticators of approved codemodules within the multi-level whitelist; and blocking the file systemor operating system activity relating to the code module when thecontent authenticator does not match any of the content authenticatorsof approved code modules within the multi-level whitelist.
 2. The methodof claim 1, wherein the code module comprises any one of an executablecode module, a dynamically-linked library file, a Java applet and aJavaScript.
 3. The method of claim 1 wherein the content authenticatorcomprises a cryptographic hash value.
 4. The method of claim 3 whereinthe cryptographic hash value is computed using any one of Message Digest#5 (MD-5), Secure Hash Algorithm (SHA), SHA-1 and SHA-256.
 5. The methodof claim 1, wherein said intercepting file system or operating systemactivity relating to a code module comprises monitoring operating systemprocess creation or module load activity.
 6. The method of claim 5,wherein the kernel mode driver is configured for operation within aMicrosoft Windows operating system.
 7. The method of claim 6, whereinsaid intercepting file system or operating system activity relating to acode module comprises an operating system module load activity monitorintercepting module load activity by running processes within thecomputer system by hooking to a Windows CreateSection API call andtemporarily turning control over to the kernel mode driver.
 8. Themethod of claim 1, wherein the multi-level whitelist further comprisesan in-memory whitelist containing content authenticators of at least asubset of the approved code modules.
 9. The method of claim 1, whereinthe file system or operating system activity relating to the code modulecomprises creating a process for the code module.
 10. The method ofclaim 1, wherein the file system or operating system activity relatingto the code module comprises loading the code module by a runningprocess.
 11. A non-transitory program storage device readable by acomputer system, tangibly embodying a program of instructions executableby one or more computer processors of the computer system to performmethod steps for authenticating dependent code modules comprising:intercepting, by a kernel mode driver of the computer system, filesystem or operating system activity relating to a code module;selectively authorizing, by the kernel mode driver, the code module byauthenticating a content authenticator of the code module with referenceto a multi-level whitelist, the multi-level whitelist comprising (i) aglobal whitelist database remote from the computer system and maintainedby a trusted service provider, the global whitelist database containingcontent authenticators of approved code modules that are known not tocontain viruses or malicious code and (ii) a local whitelist databasecontaining content authenticators of at least a subset of the approvedcode modules; allowing the file system or operating system activityrelating to the code module when the content authenticator matches oneof the content authenticators of approved code modules within themulti-level whitelist; and blocking the file system or operating systemactivity relating to the code module when the content authenticator doesnot match any of the content authenticators of approved code moduleswithin the multi-level whitelist.
 12. The program storage device ofclaim 11, wherein the code module comprises any one of an executablecode module, a dynamically-linked library file, a Java applet and aJavaScript.
 13. The program storage device of claim 11, wherein thecontent authenticator comprises a cryptographic hash value.
 14. Theprogram storage device of claim 13, wherein the cryptographic hash valueis computed using any one of Message Digest #5 (MD-5), Secure HashAlgorithm (SHA), SHA-1, SHA-256.
 15. The program storage device of claim11, wherein said intercepting file system or operating system activityrelating to a code module comprises monitoring operating system processcreation or module load activity.
 16. The program storage device ofclaim 15, wherein the kernel mode driver is configured for operationwithin a Microsoft Windows operating system.
 17. The program storagedevice of claim 16, wherein said intercepting file system or operatingsystem activity relating to a code module comprises an operating systemmodule load activity monitor intercepting module load activity byrunning processes within the computer system by hooking to a WindowsCreateSection API call and temporarily turning control over to thekernel mode driver.
 18. The program storage device of claim 11, whereinthe multi-level whitelist further comprises an in-memory whitelistcontaining content authenticators of at least a subset of the approvedcode modules.
 19. The program storage device of claim 11, wherein thefile system or operating system activity relating to the code modulecomprises creating a process for the code module.
 20. The programstorage device of claim 11, wherein the file system or operating systemactivity relating to the code module comprises loading the code moduleby a running process.